Autonomic impairment in painful neuropathy

Are the infrared thermography findings skin temperature-dependent? a study on neck pain patients

BACKGROUND

Skin temperature (Tsk) disorders have been proposed as sign of impaired innervation in several conditions, but the influence of different factors on the infrared thermography (IRT) findings remains unclear.

METHODS

The relations between the Tsk and δT (side-to-side temperature difference) values, and influence of age, gender, anthropometric characteristics and pain intensity on those values were analysed in non-specific neck pain (NP) patients (n = 91) using mixed model analysis. IRT findings were also compared in subgroups of NP patients: with cold (CHNPP, n = 21) or warm hands (WHNPP, n = 56) and healthy controls, with cold (CHC, n = 11) or warm hands (WHC, n = 19). Also, the stability of δT values in CHNPP was examined.

RESULTS

Only the area of measurement and the actual Tsk influenced the δT values. CHNPP demonstrated higher δT values in distal parts, compared with WHNPP and controls, but those values vanished when their hands turned warm. δT values in CHNPP were related to the pain intensity. The findings of WHNPP and WHC did not differ.

CONCLUSION

Our results suggest that the δT values as signs of impaired Tsk regulation are dynamic and better detectable in cold skin. The results underline the need of caution in interpretation of IRT findings.

Small fiber neuropathy: is skin biopsy the holy grail?

Small fiber neuropathy (SFN) is characterized by negative sensory symptoms (thermal and pinprick hypoesthesia) reflecting peripheral deafferentation and positive sensory symptoms and signs (burning pain, allodynia, hyperalgesia), which often dominate the clinical picture. In patients with pure SFN, clinical and neurophysiologic investigation do not show involvement of large myelinated nerve fiber making the diagnosis of SFN challenging in clinical practice. Over the last 15 years, skin biopsy has emerged as a novel tool that readily permits morphometric and qualitative evaluation of somatic and autonomic small nerve fibers. This technique has overcome the limitations of routine neurophysiologic tests to detect the damage of small nerve fibers. The recent availability of normative reference values allowed clinicians to reliably define the diagnosis of SFN in individual patients. This paper reviews usefulness and limitations of skin biopsy and the relationship between degeneration and regeneration of small nerve fibers in patients with diabetes and metabolic syndrome.

Skin innervation at different depths correlates with small fibre function but not with pain in neuropathic pain patients

BACKGROUND

Neuropathy can lead not only to impaired function but also to sensory sensitization. We aimed to link reduced skin nerve fibre density in different levels to layer-specific functional impairment in neuropathic pain patients and tried to identify pain-specific functional and structural markers.

METHODS

In 12 healthy controls and 36 patients with neuropathic pain, we assessed clinical characteristics, thermal thresholds (quantitative sensory testing) and electrically induced pain and axon reflex erythema. At the most painful sites and at intra-individual control sites, skin biopsies were taken and innervation densities in the different skin layers were assessed. Moreover, neuronal calcitonin gene-related peptide staining was quantified.

RESULTS

Perception of warm, cold and heat pain and nerve fibre density were reduced in the painful areas compared with the control sites and with healthy controls. Warm and cold detection thresholds correlated best with epidermal innervation density, whereas heat and cold pain thresholds and axon reflex flare correlated best with dermal innervation density. Clinical pain ratings correlated only with epidermal nerve fibre density (r = 0.38, p < 0.05) and better preserved cold detection thresholds (r = 0.39, p < 0.05), but not with other assessed functional and structural parameters.

CONCLUSIONS

Thermal thresholds, axon reflex measurements and assessment of skin innervation density are valuable tools to characterize and quantify peripheral neuropathy and link neuronal function to different layers of the skin. The severity of small fibre neuropathy, however, did not correspond to clinical pain intensity and a specific parameter or pattern that would predict pain intensity in peripheral neuropathy could not be identified.

Measures of small-fiber neuropathy in HIV infection

INTRODUCTION

Noninvasive methods are needed to detect distal sensory polyneuropathy in HIV-infected persons on antiretroviral therapy (ART).

METHODS

Quantitative sudomotor axon reflex test (QSART) and Utah Early Neuropathy Scale (UENS), small-fiber sensitive measures, were assessed in subjects with and without clinical neuropathy. Pain was assessed by visual analog scale (VAS).

RESULTS

Twenty-two subjects had symptoms and signs of neuropathy, 19 had neither, and all were receiving ART. Median sweat volume (μL) was lower at all testing sites in those with neuropathy compared to those without (p<0.01 for all). UENS and VAS (mm) were higher in neuropathy subjects (p<0.05 for each). Lower sweat volume at all sites correlated with higher pin UENS subscore, total UENS, and VAS (p<0.05 for all). In multivariable analyses adjusting for age, CD4⁺ T cells, sex, and use of "d-drug" ART, QSART and UENS remained associated (p=0.003).

CONCLUSION

QSART and UENS have not been previously studied in this patient population and may identify small-fiber neuropathy in HIV-infected, ART-treated persons.

Sarcoidosis and small-fiber neuropathy

Chronic pain is one of the most commonly reported symptoms among sarcoidosis patients. Not only does it significantly affect quality of life, but it also is a source of frustration for both the patient and physician because the etiology for pain often is unknown. Although patients typically complain of neuropathic-type pain, nerve conduction studies and other conventional diagnostic procedures frequently fail to reveal objective evidence of neurologic disease. However, in recent years, the growing use of specialized tests such as skin biopsy and sudomotor testing has helped to establish the diagnosis of small-fiber neuropathy as the cause of pain in these patients via objective and quantifiable means. Management of sarcoidosis small-fiber neuropathy should consist of target-directed treatment of the underlying disease and appropriate symptomatic therapy.

Complex regional pain syndrome in adults

Complex regional pain syndrome (CRPS) is a highly painful, limb-confined condition, which arises usually after trauma. It is associated with a particularly poor quality of life, and large health-care and societal costs. The causes of CRPS remain unknown. The condition's distinct combination of abnormalities includes limb-confined inflammation and tissue hypoxia, sympathetic dysregulation, small fibre damage, serum autoantibodies, central sensitization and cortical reorganization. These features place CRPS at a crossroads of interests of several disciplines including rheumatology, pain medicine and neurology. Significant scientific and clinical advances over the past 10 years hold promise both for an improved understanding of the causes of CRPS, and for more effective treatments. This review summarizes current concepts of our understanding of CRPS in adults. Based on the results from systematic reviews, treatment approaches are discussed within the context of these concepts. The treatment of CRPS is multidisciplinary and aims to educate about the condition, sustain or restore limb function, reduce pain and provide psychological intervention. Results from recent randomized controlled trials suggest that it is possible that some patients whose condition was considered refractory in the past can now be effectively treated, but confirmatory trials are required. The review concludes with a discussion of the need for additional research.

Assessment of symptomatic diabetic patients with normal nerve conduction studies: utility of cutaneous silent periods and autonomic tests

Established electrophysiological methods have limited clinical utility in the diagnosis of small-fiber neuropathy (SFN). In this study, diabetic patients with clinically diagnosed SFN were evaluated with autonomic tests and cutaneous silent periods (CSPs). Thirty-one diabetic patients with clinically suspected SFN and normal nerve conduction studies were compared with 30 controls. In the upper extremities (UE), the CSP parameters did not differ statistically between the patient and control groups, whereas, in the lower extremities (LE), patients had prolonged CSP latencies (P = 0.018) and shortened CSP durations (P < 0.001). The sensitivity of the CSP duration was 32.6%, and the specificity was 96.7%. The expiration-to-inspiration ratios and amplitudes of the sympathetic skin responses in the lower extremities were also reduced. Our findings indicate that the diagnostic utility of CSPs was higher than that of the autonomic tests to support the clinically suspected diagnosis of SFN.

European Federation of Neurological Societies/Peripheral Nerve Society Guideline on the use of skin biopsy in the diagnosis of small fiber neuropathy. Report of a joint task force of the European Federation of Neurological Societies and the Peripheral Nerve Society

BACKGROUND

Revision of the guidelines on the use of skin biopsy in the diagnosis of peripheral neuropathy, published in 2005, has become appropriate owing to publication of more relevant articles. Most of the new studies focused on small fiber neuropathy (SFN), a subtype of neuropathy for which the diagnosis was first developed through skin biopsy examination. This revision focuses on the use of this technique to diagnose SFN.

METHODS

Task force members searched the Medline database from 2005, the year of the publication of the first EFNS guideline, to June 30th, 2009. All pertinent articles were rated according to the EFNS and PNS guidance. After a consensus meeting, the task force members created a manuscript that was subsequently revised by two experts (JML and JVS) in the field of peripheral neuropathy and clinical neurophysiology, who were not previously involved in the use of skin biopsy.

RESULTS AND CONCLUSIONS

Distal leg skin biopsy with quantification of the linear density of intraepidermal nerve fibers (IENF), using generally agreed upon counting rules, is a reliable and efficient technique to assess the diagnosis of SFN (Recommendation Level A). Normative reference values are available for bright-field immunohistochemistry (Recommendation Level A) but not yet for confocal immunofluorescence or the blister technique. The morphometric analysis of IENF density, either performed with bright-field or immunofluorescence microscopy, should always refer to normative values matched for age (Recommendation Level A). Newly established laboratories should undergo adequate training in a well-established skin biopsy laboratory and provide their own stratified for age and gender normative values, intra- and interobserver reliability, and interlaboratory agreement. Quality control of the procedure at all levels is mandatory (Good Practice Point). Procedures to quantify subepidermal nerve fibers and autonomic innervated structures, including erector pili muscles, and skin vessels, are under development but need to be confirmed by further studies. Sweat gland innervation can be examined using an unbiased stereologic technique recently proposed (Recommendation Level B). A reduced IENF density is associated with the risk of developing neuropathic pain (Recommendation Level B), but it does not correlate with its intensity. Serial skin biopsies might be useful for detecting early changes of IENF density, which predict the progression of neuropathy, and to assess degeneration and regeneration of IENF (Recommendation Level C). However, further studies are warranted to confirm its potential usefulness as an outcome measure in clinical practice and research. Skin biopsy has not so far been useful for identifying the etiology of SFN. Finally, we emphasize that 3-mm skin biopsy at the ankle is a safe procedure based on the experience of 10 laboratories reporting absence of serious side effects in approximately 35,000 biopsies and a mere 0.19% incidence of non-serious side effects in about 15 years of practice (Good Practice Point).

Comparison of sudomotor and sensory nerve testing in painful sensory neuropathies

OBJECTIVE

To compare results of quantitative sudomotor axon reflex testing (QSART), dorsal sural, and sural sensory nerve testing in patients with painful sensory neuropathy (PSN).

METHODS

Fifty-six patients with symptoms and neurologic examinations consistent with PSN who had both autonomic and nerve conduction studies were identified from 376 patients with a clinical diagnosis of painful neuropathy. Cases were clinically categorized as large-fiber or small-fiber neuropathies by described criteria. The results of sural, dorsal sural, and QSART tests were then analyzed in relationship to these two clinical groups.

RESULTS

Evidence of unmyelinated fiber abnormalities by QSART was noted in 85% of clinical large-fiber and 69% of clinical small-fiber groups. Dorsal sural potentials were absent in all the large-fiber group but also in 52% of clinically classified small-fiber neuropathies. When QSART and dorsal sural abnormalities were combined, the identification of abnormalities in all the cases of PSN was 89% with 75% of cases (42) showing mixed large and small fiber abnormalities, 14% unmyelinated sensory fiber abnormalities (by QSART), and 11% normal studies.

CONCLUSION

This study demonstrates the value of combining both QSART and dorsal sural sensory testing in verifying the diagnosis of PSN. The majority of cases demonstrate involvement of unmyelinated C fibers as well as large/medium myelinated fibers, thereby separating mixed large- and small-fiber sensory neuropathies from those cases classified by clinical criteria solely as small-fiber neuropathy.

Autonomic testing: common techniques and clinical applications

Laboratories able to test autonomic function are increasingly available and rely on batteries of well-accepted, noninvasive tests. Tests of parasympathetic cardiovagal, sympathetic vasoconstriction, and sudomotor (sweating) function are most commonly employed. Common examples include heart rate variability to various challenges, Valsalva maneuver, standing and tilt-table studies, and various sudomotor methods. New techniques and technical refinements continue to be described. Most studies rely on perturbations of complex systems and not direct assessment. Testing has helped to improve disease recognition and prompted advances in classification, pathophysiology, and treatment. Major areas impacted include hereditary and immune-mediated autonomic neuropathy, diabetic autonomic neuropathy, distal symmetric polyneuropathy, Parkinson disease and other autonomic failure syndromes, orthostatic intolerance, and unexplained syncope.

Peripheral nervous system manifestations of Sjögren syndrome: clinical patterns, diagnostic paradigms, etiopathogenesis, and therapeutic strategies

Sjögren syndrome is among the most common autoimmune diseases affecting adults in the United States, and is frequently regarded as an immune-mediated exocrinopathy exclusively causing dry eyes and dry mouth. However, as a systemic rheumatic disease, there can be various "extraglandular" complications. The eclectic permutation of peripheral nervous system (PNS) syndromes which occur in Sjögren patients are among the most common and severe extraglandular complications. This review article highlights the evaluation, differential diagnosis, immunopathogenic mechanisms, and potential treatment options of these PNS complications encountered by neurologists. The sensory neuropathies constitute the most frequent PNS complication. Sjögren patients can suffer from severe neuropathic pain, with small-fiber neuropathy causing lancinating or burning pain which can disproportionately affect the proximal torso or extremities, and the face (ie, in a "non-length-dependent distribution"). The technique of skin biopsy, assessing for the intraepidermal nerve fiber density of unmyelinated nerves, provides a useful technique for neurologists to diagnose small-fiber neuropathies, especially when there is such a non-length-dependent distribution. Other diagnostic techniques (ie, electromyography/nerve-conduction studies, evoked potentials, nerve and muscle biopsy) may be useful in specific subtypes of neuropathies. A rational approach to treatment requires a careful appraisal of the clinical subtype of the neuropathy, as well as a familiarity with such discriminating immunopathogenic mechanisms. The application of the traditional armamentarium used for neuropathic pain can be especially challenging. Sjögren patients can suffer from debilitating fatigue, sicca symptoms, and autonomic findings; as such manifestations can be complications of various neuropathic agents, neurologists should understand how to minimize such iatrogenic complications. Therefore, this article will empower neurologists to more effectively collaborate with rheumatologists, in the diagnosis and treatment of Sjögren patients with PNS complications.

Utility of skin biopsy to evaluate peripheral neuropathy

Skin biopsy for epidermal nerve fiber analysis provides an important objective test for the diagnosis of peripheral neuropathy, particularly small fiber sensory neuropathy (SFSN). The determination of epidermal nerve fiber density (ENFD) is reliable, with high diagnostic specificity and good sensitivity. Because of false negatives, biopsy results must be interpreted in conjunction with neurologic findings and laboratory results, including objective tests of sensory and autonomic function. SFSN most commonly is length dependent and is idiopathic in about half the patients. Biopsy of a proximal site (thigh) and a distal site (calf) typically shows greater abnormality of ENFD distally than proximally. More severe abnormality of ENFD in the thigh than in the calf raises the possibility of a non-length-dependent SFSN. The causes of this type of neuropathy, such as Sjögren's syndrome, sarcoidosis, and celiac disease, may be treatable.

Impaired heart rate recovery index in patients with sarcoidosis

BACKGROUND

Sarcoidosis, an inflammatory granulomatous disease, is associated with various cardiac disorders, including threatening ventricular arrhythmias and sudden cardiac death. Heart rate recovery (HRR) after exercise is a function of vagal reactivation, and its impairment is an independent prognostic indicator for cardiovascular and all-cause mortality. The aim of our study was to evaluate HRR in patients with sarcoidosis.

METHODS

The study population included 56 patients with sarcoidosis (23 men, mean age = 47.3 ± 13.0 years, and mean disease duration = 38.4 ± 9.7 months) and 54 healthy control subjects (20 men, mean age = 46.5 ± 12.9 years). Basal ECG, echocardiography, and treadmill exercise testing were performed on all patients and control participants. The HRR index was defined as the reduction in the heart rate at peak exercise to the first-minute rate (HRR(1)), second-minute (HRR(2)), third-minute (HRR(3)), and fifth-minute (HRR(5)) after the cessation of exercise stress testing.

RESULTS

There are significant differences in HRR(1) and HRR(2) indices between patients with sarcoidosis and the control group (25 ± 6 vs 34 ± 11; P < .001 and 45 ± 10 vs 53 ± 12; P < .001, respectively). Similarly, HRR(3) and HRR(5) indices of the recovery period were lower in patients with sarcoidosis when compared with indices in the control group (53 ± 12 vs 61 ± 13; P < .001 and 60 ± 13 vs 68 ± 13; P < .001, respectively). Exercise capacity was notably lower (9.2 ± 2.1 vs 11.6 ± 2.8 METs; P = .001, respectively) and systolic pulmonary arterial pressure at rest was significantly higher in patients with sarcoidosis compared with the control group (29.7 ± 5.5 mm Hg vs 25.6 ± 5.7 mm Hg, P = .001, respectively). Furthermore, HRR indices were found to be different among radiographic stage groups.

CONCLUSIONS

The HRR index was impaired in patients with sarcoidosis as compared with control subjects. When the prognostic significance of the HRR index is considered, these results may partially explain the increased occurrence of arrhythmias and sudden cardiac death in patients with sarcoidosis. Our findings suggest that the HRR index may be clinically helpful in identifying high-risk patients with sarcoidosis.

Primary Raynaud phenomenon and small-fiber neuropathy: is there a connection? A pilot neurophysiologic study

The pathophysiologic factors of primary Raynaud phenomenon (RP) are unknown. Preliminary evidence from skin biopsy suggests small-fiber neuropathy (SFN) in primary RP. We aimed to quantitatively assess SFN in participants with primary RP. Consecutive patients with an a priori diagnosis of primary RP presenting to our outpatient rheumatology clinic over a 6-month period were invited to participate. Cases of secondary RP were excluded. All participants were required to have normal results on nailfold capillary microscopy. Assessment for SFN was accomplished with autonomic reflex screening, which includes quantitative sudomotor axonal reflex test (QSART), and cardiovagal and adrenergic function testing, thermoregulatory sweat test (TST), and quantitative sensory test (QST) for vibratory, cooling, and heat-pain sensory thresholds. Nine female participants with a median age of 38 years (range 21-46 years) and a median symptom duration of 9 years (range 5 months-31 years) were assessed. Three participants had abnormal results on QSART, indicating peripheral sudomotor autonomic dysfunction. Two participants had evidence of large-fiber involvement with heat-pain thresholds on QST. Heart rate and blood pressure responses to deep breathing, Valsalva maneuver, and 70° tilt were normal for all participants. Also, all participants had normal TST results. In total, three of the nine participants had evidence of SFN. The presence of SFN raises the possibility that a subset of patients with primary RP have an underlying, subclinical small-fiber dysfunction. These data open new avenues of research and therapeutics for this common condition.

Practice parameter: the evaluation of distal symmetric polyneuropathy: the role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review). Report of the American Academy of Neurology, the American Association of Neuromuscular and Electrodiagnostic Medicine, and the American Academy of Physical Medicine and Rehabilitation

BACKGROUND

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence-based guidelines regarding the role of autonomic testing, nerve biopsy and skin biopsy for the assessment of polyneuropathy.

METHODS

A literature review using MEDLINE, EMBASE, Science Citation Index and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four-tiered level of evidence scheme and recommendations were based upon the level of evidence.

RESULTS AND CONCLUSIONS

1. Autonomic testing may be considered in the evaluation of patients with polyneuropathy to document autonomic nervous system dysfunction (Level B). Such testing should be considered especially for the evaluation of suspected autonomic neuropathy (Level B) and distal small fiber sensory polyneuropathy (SFSN) (Level C). A battery of validated tests is recommended to achieve the highest diagnostic accuracy (Level B). 2. Nerve biopsy is generally accepted as useful in the evaluation of certain neuropathies as in patients with suspected amyloid neuropathy, mononeuropathy multiplex due to vasculitis, or with atypical forms of chronic inflammatory demyelinating polyneuropathy (CIDP). However, the literature is insufficient to provide a recommendation regarding when a nerve biopsy may be useful in the evaluation of DSP (Level U). 3. Skin biopsy is a validated technique for determining intraepidermal nerve fiber (IENF) density and may be considered for the diagnosis of DSP, particularly SFSN (Level C). There is a need for additional prospective studies to define more exact guidelines for the evaluation of polyneuropathy.

Evaluation of distal symmetric polyneuropathy: the role of autonomic testing, nerve biopsy, and skin biopsy (an evidence-based review)

Distal symmetric polyneuropathy (DSP) is the most common variety of neuropathy. Since the evaluation of this disorder is not standardized, the available literature was reviewed to provide evidence-based guidelines regarding the role of autonomic testing, nerve biopsy, and skin biopsy for the assessment of polyneuropathy. A literature review using MEDLINE, EMBASE, Science Citation Index, and Current Contents was performed to identify the best evidence regarding the evaluation of polyneuropathy published between 1980 and March 2007. Articles were classified according to a four-tiered level of evidence scheme and recommendations were based on the level of evidence. (1) Autonomic testing may be considered in the evaluation of patients with polyneuropathy to document autonomic nervous system dysfunction (Level B). Such testing should be considered especially for the evaluation of suspected autonomic neuropathy (Level B) and distal small fiber sensory polyneuropathy (SFSN) (Level C). A battery of validated tests is recommended to achieve the highest diagnostic accuracy (Level B). (2) Nerve biopsy is generally accepted as useful in the evaluation of certain neuropathies as in patients with suspected amyloid neuropathy, mononeuropathy multiplex due to vasculitis, or with atypical forms of chronic inflammatory demyelinating polyneuropathy (CIDP). However, the literature is insufficient to provide a recommendation regarding when a nerve biopsy may be useful in the evaluation of DSP (Level U). (3) Skin biopsy is a validated technique for determining intraepidermal nerve fiber (IENF) density and may be considered for the diagnosis of DSP, particularly SFSN (Level C). There is a need for additional prospective studies to define more exact guidelines for the evaluation of polyneuropathy.

Other autonomic neuropathies associated with ganglionic antibody

The acetylcholine receptor ganglionic (G-AchR) antibody is a very specific serologic test for autoimmune autonomic ganglionopathy. The spectrum of autoimmune (or presumed to be autoimmune) autonomic disorders, however, is quite broad and positivity to this antibody has been reported in a variety of other conditions, albeit infrequent and with low titer. This review describes the autonomic neuropathies most frequently encountered in clinical practice in which an autoimmune etiology is suspected. They include a chronic form (pure autonomic failure) and limited autonomic neuropathies with predominant involvement of one neurotransmitter type (i.e., cholinergic vs. adrenergic) or one system (such as the gastrointestinal system) or a distal small fiber dysfunction. In each of these conditions, occasional positivity to the G-AchR antibody has been found, but the pathogenetic significance of such finding is still uncertain. Other antigens and antibodies yet to be identified are more likely to be responsible in these disorders.

Pitfalls of diagnostic criteria for small fiber neuropathy

This Practice Point commentary discusses a retrospective study conducted by Devigili et al. that sought to establish gold standard diagnostic criteria for small fiber neuropathy (SFN). The chosen gold standard for SFN requires abnormalities on two out of three tests (clinical findings, skin biopsy [epidermal nerve fiber density] and quantitative sensory testing), with nerve conduction studies being normal. A total of 150 patients with sensory symptoms met study inclusion criteria, and 67 were determined to have SFN on the basis of the gold standard criteria. Epidermal nerve fiber density was the single most useful test for SFN with a diagnostic efficiency of 88.4%. This commentary argues in favor of a hierarchical system of levels of diagnostic certainty for SFN, depending on the number and type of abnormal diagnostic tests, in contrast to the dichotomous approach used by Devigili et al. We further highlight methodological limitations of the present study, such as the confounding of diagnostic-efficiency estimates for individual SFN tests through incorporation bias.

The diagnostic criteria for small fibre neuropathy: from symptoms to neuropathology

Small fibre neuropathy (SFN), a condition dominated by neuropathic pain, is frequently encountered in clinical practise either as prevalent manifestation of more diffuse neuropathy or distinct nosologic entity. Aetiology of SFN includes pre-diabetes status and immune-mediated diseases, though it remains frequently unknown. Due to their physiologic characteristics, small nerve fibres cannot be investigated by routine electrophysiological tests, making the diagnosis particularly difficult. Quantitative sensory testing (QST) to assess the psychophysical thresholds for cold and warm sensations and skin biopsy with quantification of somatic intraepidermal nerve fibres (IENF) have been used to determine the damage to small nerve fibres. Nevertheless, the diagnostic criteria for SFN have not been defined yet and a 'gold standard' for clinical practise and research is not available. We screened 486 patients referred to our institutions and collected 124 patients with sensory neuropathy. Among them, we identified 67 patients with pure SFN using a new diagnostic 'gold standard', based on the presence of at least two abnormal results at clinical, QST and skin biopsy examination. The diagnosis of SFN was achieved by abnormal clinical and skin biopsy findings in 43.3% of patients, abnormal skin biopsy and QST findings in 37.3% of patients, abnormal clinical and QST findings in 11.9% of patients, whereas 7.5% patients had abnormal results at all the examinations. Skin biopsy showed a diagnostic efficiency of 88.4%, clinical examination of 54.6% and QST of 46.9%. Receiver operating characteristic curve analysis confirmed the significantly higher performance of skin biopsy comparing with QST. However, we found a significant inverse correlation between IENF density and both cold and warm thresholds at the leg. Clinical examination revealed pinprick and thermal hypoesthesia in about 50% patients, and signs of peripheral vascular autonomic dysfunction in about 70% of patients. Spontaneous pain dominated the clinical picture in most SFN patients. Neuropathic pain intensity was more severe in patients with SFN than in patients with large or mixed fibre neuropathy, but there was no significant correlation with IENF density. The aetiology of SFN was initially unknown in 41.8% of patients and at 2-year follow-up a potential cause could be determined in 25% of them. Over the same period, 13% of SFN patients showed the involvement of large nerve fibres, whereas in 45.6% of them the clinical picture did not change. Spontaneous remission of neuropathic pain occurred in 10.9% of SFN patients, while it worsened in 30.4% of them.

The Neuropad test: a visual indicator test for human diabetic neuropathy

AIMS/HYPOTHESIS

The commercially available Neuropad test was developed as a simple visual indicator test to evaluate diabetic neuropathy. It uses a colour change to define the integrity of skin sympathetic cholinergic innervation. We compared the results of Neuropad assessment in the foot with established measures of somatic and autonomic neuropathy.

METHODS

Fifty-seven diabetic patients underwent Neuropad assessment, quantitative sensory and autonomic function testing, and evaluation of intra-epidermal nerve fibre density in foot skin biopsies.

RESULTS

Neuropad responses correlated with the neuropathy disability score (r(s)=0.450, p<0.001), neuropathic symptom score (r(s)=0.288, p=0.03), cold detection threshold (r(s)=0.394, p = 0.003), heat-as-pain perception threshold visual analogue score 0.5 (r(s)=0.279, p=0.043) and deep-breathing heart rate variability (r(s)= -0.525, p<0.001). Intra-epidermal nerve fibre density (fibres/mm) compared with age- and sex-matched control subjects (11.06+/-0.82) was non-significantly reduced (7.37+/-0.93) in diabetic patients with a normal Neuropad response and significantly reduced in patients with a patchy (5.01+/-0.93) or absent (5.02+/-0.77) response (p=0.02). The sensitivity of an abnormal Neuropad response in detecting clinical neuropathy (neuropathy disability score >or=5) was 85% (negative predictive value 71%) and the specificity was 45% (positive predictive value 69%).

CONCLUSIONS/INTERPRETATION

The Neuropad test may be a simple indicator for screening patients with diabetic neuropathy.

Recurrent postoperative CRPS I in patients with abnormal preoperative sympathetic function

PURPOSE

A complex regional pain syndrome of an extremity that has previously resolved can recur after repeat surgery at the same anatomic site. Complex regional pain syndrome is described as a disease of the autonomic nervous system. The purpose of this study was to evaluate preoperative and postoperative sympathetic function and the recurrence of complex regional pain syndrome type I (CRPS I) in patients after repeat carpal tunnel surgery.

METHODS

Thirty-four patients who developed CRPS I after initial carpal tunnel releases and required repeat open carpal tunnel surgeries were studied. Laser Doppler imaging (LDI) was used to assess preoperative sympathetic function 5-7 days prior to surgery and to assess postoperative sympathetic function 19-22 days after surgery or 20-22 days after resolution of the CRPS I. Sympathetic nervous system function was prospectively examined by testing reflex-evoked vasoconstrictor responses to sympathetic stimuli recorded with LDI of both hands. Patients were assigned to 1 of 2 groups based on LDI responses to sympathetic provocation. Group I (11 of 34) patients had abnormal preoperative LDI studies in the hands that had prior surgeries, whereas group II (23 of 34) patients had normal LDI studies. Each patient in this study had open repeat carpal tunnel surgery.

RESULTS

In group I, 8 of 11 patients had recurrent CRPS I, whereas in group II, 3 of 23 patients had recurrent CRPS I. All of the recurrent CRPS I patients were successfully treated with sympathetic blockade, occupational therapy, and pharmacologic modalities. Repeat LDI after recurrent CRPS I resolution was abnormal in 8 of 8 group I patients and in 1 of 3 group II patients.

CONCLUSIONS

CRPS I can recur after repeat hand surgery. Our study results may, however, identify those individuals who may readily benefit from perioperative therapies.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic I.

Diagnostic validity of epidermal nerve fiber densities in painful sensory neuropathies

In this prospective study, intraepidermal nerve fiber densities (IENFD) and subepidermal nerve plexus densities (SENPD) were quantified by immunostaining in skin punch biopsies from the distal calf in 99 patients with clinical symptoms of painful sensory neuropathy and from 37 age-matched healthy volunteers. The clinical diagnosis was based on history and abnormal thermal thresholds on quantitative sensory testing (QST). In patients with neuropathy, IENFD and SENPD were reduced to about 50% of controls. Elevated warm detection thresholds on QST correlated with IENFD but not with SENPD. Using receiver-operating characteristic (ROC) curve analysis of IENFD values, the diagnostic sensitivity for detecting neuropathy was 0.80 and the specificity 0.82. For SENPD, sensitivity was 0.81 and specificity 0.88. With ROC analysis of both IENFD and SENPD together, the diagnostic sensitivity was further improved to 0.92. The combined examination of IENFD and SENPD is a highly sensitive and specific diagnostic tool in patients suspected to suffer from painful sensory neuropathies but with normal values on clinical neurophysiological studies.

Skin biopsy as a diagnostic tool in peripheral neuropathy

Skin biopsy is a safe, minimally invasive, painless and cheap tool for providing diagnostic information on small nerve fibers, which are invisible to routine neurophysiological tests. Biopsy can be performed in hairy skin to investigate unmyelinated and thinly myelinated fibers and in glabrous skin to examine large myelinated fibers. Morphometric analysis of skin nerves is readily accomplished through the use of immunohistochemical techniques, and has proved to be reliable, reproducible and unaffected by the severity of neuropathy. One further advantage of skin biopsy over conventional nerve biopsy is that it allows somatic nerve fibers to be distinguished from autonomic nerve fibers. Morphological changes, axonal degeneration and abnormal regeneration occur in cutaneous nerves very early in the course of peripheral neuropathies, making skin biopsy a promising tool for investigating the progression of neuropathy and the effect of neuroprotective treatments in clinical practice and trials. This article reviews the techniques that are used to investigate the innervation of human skin, the possible uses of skin biopsy in diagnosing and monitoring peripheral neuropathies, and correlations between skin biopsy findings and those of other diagnostic methods.

The diagnostic workup of patients with neuropathic pain

Neuropathic pain is initiated or caused by damage or dysfunction of the peripheral or central nervous systems in various disorders, each having pain-related symptoms and signs thought secondary to common pain mechanisms. Ancillary testing may demonstrate associated nervous system abnormalities, however its specificity is inadequate at present, as it makes inferential conclusions from indirect data. Symptom assessment and physical findings remain paramount in the diagnosis of neuropathic pain.

Skin biopsy in the management of peripheral neuropathy

Skin biopsy has been widely used in recent years for the investigation of small-calibre sensory nerves, including somatic unmyelinated intraepidermal nerve fibres, dermal myelinated nerve fibres, and autonomic nerve fibres in peripheral neuropathies, with different techniques for tissue processing and nerve fibre assessment. Here, we review the techniques for skin biopsy, the processing and assessment of the biopsy sample, their possible uses in different types of peripheral neuropathy, and their use in the follow-up of patients and in clinical trials. We also review the association between morphological measures of skin innervation and function and the limits of this method in the aetiological classification of peripheral neuropathies.

The diagnostic workup of patients with neuropathic pain

Determining the causes of neuropathic pain is more than an epistemological exercise. At its essence, it is a quest to delineate mechanisms of dysfunction through which treatment strategies can be created that are effective in reducing, ameliorating, or eliminating symptomatology. To date, predictors of which patients will develop neuropathic pain or who will respond to specific therapies are lacking, and present therapies have been developed mainly through trial and error. Our current inability to make therapeutically meaningful decisions based on ancillary test data is illustrated by the following: In a study specifically designed to assess the response of patients with painful distal sensory neuropathies to the 5% lidocaine patch, no relationship between treatment response and distal leg skin biopsy, QST, or sensory nerve conduction study results could be established. From a mechanistic perspective, the hypothesis that the lidocaine patch would be most effective in patients with relatively intact epidermal innervation, whose neuropathic pain is presumed attributable to "irritable nociceptors," and least effective in patients with few surviving epidermal nociceptors, presumably with "deafferentation pain," was unproven. The possible explanations are multiple and outside the scope of this review. However, these findings, coupled with the disparity in C-fiber subtype involvement in diabetic small-fiber neuropathy, and the recently reported inability of enzyme replacement therapy in Fabry disease to influence intraepidermal innervation density, while having mixed effects on cold and warm QST thresholds, and beneficial effects on sudomotor findings, when therapeutic benefit was demonstrated, lead one to conclude that the specificity of ancillary testing in neuropathic pain is inadequate at present, and reinforce the aforementioned caveats about inferential conclusions from indirect data. The diagnosis of neuropathic pain mechanisms is in its nascent stages and ancillary testing remains "subordinate," "subsidiary," and "auxiliary" as defined in Webster's Third New International Dictionary. As a consequence of these difficulties, the recent approach by Bennett and his colleagues may have merit. They have hypothesized (and provide data in support) that chronic pain can be more or less neuropathic on a spectrum between "likely," "possible," and "unlikely," based on patient responses on validated neuropathic pain symptom scales, when compared with specialist pain physician certainty of the presence of neuropathic pain on a 100-mm visual analog scale. The symptoms most associated with neuropathic pain were dysesthesias, evoked pain, paroxysmal pain, thermal pain, autonomic complaints, and descriptions of the pain as being sharp, hot, or cold, with high sensitivity. Higher scores for these symptoms correlated with greater clinician certainty of the presence of neuropathic pain mechanisms. Considering each individual patient's chronic pain as being somewhere on a continuum between "purely nociceptive" and "purely neuropathic" may have diagnostic and therapeutic relevance by enhancing specificity, but this requires clinical confirmation. Thus, symptom assessment remains indispensable in the evaluation of neuropathic pain, ancillary testing notwithstanding

Detection of small-fiber neuropathy by sudomotor testing

The symptoms of burning sensation affecting the feet, thought to be due to a distal small-fiber neuropathy (DSFN) affecting somatic unmyelinated fibers, are usually accompanied by vasomotor or sudomotor changes suggestive of involvement of autonomic fibers. We therefore examined the relationship between pattern of anhidrosis and DSFN and its etiology, comparing patients with "pure" DSFN (with normal nerve conduction) to those with clinical DSFN (minor conduction abnormalities). We reviewed 125 cases with a clinical phenotype of DSFN. These patients had distal burning discomfort, variable sensory deficits, and intact motor function. All had undergone assessment with thermoregulatory sweat test (TST), autonomic reflex screen (ARS), and nerve conduction studies and electromyography (NCS/EMG). TST showed a distal pattern of anhidrosis in 74%. The quantitative sudomotor axon reflex test (QSART) was abnormal in 74%, with 80% of those having a length-dependent pattern of anhidrosis/hypohidrosis. In total, 93% of patients had a distal pattern of abnormality on QSART or TST. The Composite Autonomic Severity Score (CASS) was used to quantify the severity and distribution of autonomic deficits: 98% had CASS abnormality (sudomotor, 98%; adrenergic, 43%; cardiovagal, 35%). EMG was normal or showed unrelated abnormalities in 75%. The most common etiologies of DSFN were idiopathic (73%), presumed hereditary (18%), and diabetes (10%). Sudomotor examination is thus a highly sensitive detection tool in DSFN. Autonomic involvement is mainly distal, and additionally may involve adrenergic and the long cardiovagal fibers.

Small-fiber neuropathy: answering the burning questions

Small-fiber neuropathy is a peripheral nerve disease that most commonly presents in middle-aged and older people, who develop burning pain in their feet. Although it can be caused by disorders of metabolism such as diabetes, chronic infections (such as with human immunodeficiency virus), genetic abnormalities, toxicity from various drugs, and autoimmune diseases, the cause often remains a mystery because standard electrophysiologic tests for nerve injury do not detect small-fiber function. Inadequate ability to test for and diagnose small-fiber neuropathies has impeded patient care and research, but new tools offer promise. Infrequently, the underlying cause of small-fiber dysfunction is identified and disease-modifying therapy can be instituted. More commonly, the treatments for small-fiber neuropathy involve symptomatic treatment of neuropathic pain.

Intraepidermal nerve fibre density, quantitative sensory testing and nerve conduction studies in a patient material with symptoms and signs of sensory polyneuropathy

Small diameter nerve fibre (SDNF) neuropathy is an axonal sensory neuropathy affecting unmyelinated (C) and thin myelinated (A-delta) fibres. We have evaluated 75 patients with symptoms and signs suggesting SDNF dysfunction with or without symptoms and signs of co-existing large diameter nerve fibre involvement. The patients were examined clinically and underwent skin biopsy, quantitative sensory testing (QST) and nerve conduction studies (NCS). The purpose of this study was to compare the relationship between the different methods and in particular measurements of thermal thresholds and intraepidermal nerve fibre (IENF) density in the same site of the distal leg. The main subdivision of the patient material was made according to the overall NCS pattern. Patients with normal NCS (38) had 6.4 +/- 3.8 and patients with abnormal NCS (37) had 4.4 +/- 3.4 IENF per mm (P = 0.02). Limen (difference between warm and cold perception thresholds) was significantly higher (more abnormal) in those with abnormal than in those with normal NCS (22.1 +/- 9.1 vs. 13.4 +/- 5.6, P < 0.0001). Cold perception threshold was more abnormal (P < 0.0001) than warm perception threshold (P = 0.002). Correlation between IENF and QST was statistically significant only when NCS was abnormal, and thus dependent of a more severe neuropathic process in SDNFs.

Immune-mediated autonomic neuropathies

Improved recognition and availability of noninvasive testing of autonomic disorders has prompted a better understanding of disease mechanisms of some disease forms, especially potentially treatable immune-mediated autonomic neuropathies. Development is acute, subacute, or less commonly chronic. Autonomic involvement is common and an important cause of morbidity and mortality in Guillain-Barré syndrome. Acute autonomic neuropathy can affect parasympathetic, sympathetic, and enteric nerves or neurons and is associated with antibodies to ganglionic nicotinic acetylcholine receptors. These antibodies appear to be causative based on a rabbit immunization model and serum transfer studies from patients and animals. Other important immune autonomic disorders discussed include Lambert-Eaton myasthenic syndrome, some forms of orthostatic intolerance, chronic autonomic neuropathy, and Sjögren syndrome. Paraneoplastic autonomic disorders are clinically indistinguishable and associated with various overlapping antibody associations, including anti-Hu (ANNA-1), ganglionic acetylcholine receptors, CRMP-5, and PCA-2.

Evidence of focal small-fiber axonal degeneration in complex regional pain syndrome-I (reflex sympathetic dystrophy)

CRPS-I consists of post-traumatic limb pain and autonomic abnormalities that continue despite apparent healing of inciting injuries. The cause of symptoms is unknown and objective findings are few, making diagnosis and treatment controversial, and research difficult. We tested the hypotheses that CRPS-I is caused by persistent minimal distal nerve injury (MDNI), specifically distal degeneration of small-diameter axons. These subserve pain and autonomic function. We studied 18 adults with IASP-defined CRPS-I affecting their arms or legs. We studied three sites on subjects' CRPS-affected and matching contralateral limb; the CRPS-affected site, and nearby unaffected ipsilateral and matching contralateral control sites. We performed quantitative mechanical and thermal sensory testing (QST) followed by quantitation of epidermal neurite densities within PGP9.5-immunolabeled skin biopsies. Seven adults with chronic leg pain, edema, disuse, and prior surgeries from trauma or osteoarthritis provided symptom-matched controls. CRPS-I subjects had representative histories and symptoms. Medical procedures were unexpectedly frequently associated with CRPS onset. QST revealed mechanical allodynia (P<0.03) and heat-pain hyperalgesia (P<0.04) at the CRPS-affected site. Axonal densities were highly correlated between subjects' ipsilateral and contralateral control sites (r=0.97), but were diminished at the CRPS-affected sites of 17/18 subjects, on average by 29% (P<0.001). Overall, control subjects had no painful-site neurite reductions (P=1.00), suggesting that pain, disuse, or prior surgeries alone do not explain CRPS-associated neurite losses. These results support the hypothesis that CRPS-I is specifically associated with post-traumatic focal MDNI affecting nociceptive small-fibers. This type of nerve injury will remain undetected in most clinical settings.

EFNS guidelines on the use of skin biopsy in the diagnosis of peripheral neuropathy

Skin biopsy has become a widely used tool to investigate small calibre sensory nerves including somatic unmyelinated intraepidermal nerve fibres (IENF), dermal myelinated nerve fibres, and autonomic nerve fibres in peripheral neuropathies and other conditions. Different techniques for tissue processing and nerve fibre evaluation have been used. In March 2004, a Task Force was set up under the auspices of the European Federation of Neurological Societies (EFNS) with the aim of developing guidelines on the use of skin biopsy in the diagnosis of peripheral neuropathies. We searched the Medline database from 1989, the year of the first publication describing the innervation of human skin using immunostaining with anti-protein-gene-product 9.5 (PGP 9.5) antibodies, to 31 March 2005. All pertinent papers were rated according to the EFNS guidance. The final version of the guidelines was elaborated after consensus amongst members of the Task Force was reached. For diagnostic purposes in peripheral neuropathies, we recommend performing a 3-mm punch skin biopsy at the distal leg and quantifying the linear density of IENF in at least three 50-mum thick sections per biopsy, fixed in 2% PLP or Zamboni's solution, by bright-field immunohistochemistry or immunofluorescence with anti-PGP 9.5 antibodies (level A recommendation). Quantification of IENF density closely correlated with warm and heat-pain threshold, and appeared more sensitive than sensory nerve conduction study and sural nerve biopsy in diagnosing small-fibre sensory neuropathy. Diagnostic efficiency and predictive values of this technique were very high (level A recommendation). Confocal microscopy may be particularly useful to investigate myelinated nerve fibres, dermal receptors and dermal annex innervation. In future, the diagnostic yield of dermal myelinated nerve fibre quantification and of sweat gland innervation should be addressed. Longitudinal studies of IENF density and regeneration rate are warranted to correlate neuropathological changes with progression of neuropathy and to assess the potential usefulness of skin biopsy as an outcome measure in peripheral neuropathy trials (level B recommendation). In conclusion, punch skin biopsy is a safe and reliable technique (level A recommendation). Training in an established cutaneous nerve laboratory is recommended before using skin biopsy as a diagnostic tool in peripheral neuropathies. Quality control at all levels is mandatory.

Skin denervation and cutaneous vasculitis in systemic lupus erythematosus

To understand the clinical significance and mechanisms of cutaneous denervation in systemic lupus erythematosus (SLE), we assessed intraepidermal nerve fibre (IENF) density of the distal leg in 45 SLE patients (4 males and 41 females, aged 38.4 +/- 13.6 years) and analysed its correlations with pathology, lupus activity, sensory thresholds and electrophysiological parameters. Compared with age- and gender-matched control subjects, SLE patients had lower IENF densities (3.08 +/- 2.17 versus 11.27 +/- 3.96 fibres/mm, P < 0.0001); IENF densities were reduced in 38 patients (82.2%). Pathologically, 11 patients (24.4%) were found to have definite cutaneous vasculitis; the severity and extent of cutaneous vasculitis were correlated with IENF densities. Patients with active lupus had even lower IENF densities than those with quiescent lupus (1.86 +/- 1.37 versus 4.15 +/- 2.20 fibres/mm, P = 0.0002). By linear regression analysis, IENF densities were negatively correlated with the SLE disease activity index (r = 0.527, P = 0.0002) and cumulative episodes of lupus flare-up within 2 years before the skin biopsy (r = 0.616, P = 0.0014). Clinically, skin denervation was present not only in the patients with sensory neuropathy but also in the patients with neuropsychiatric syndrome involving the CNS. SLE patients had significantly elevated warm threshold temperatures (P = 0.003) and reduced cold threshold temperatures (P = 0.048); elevated warm threshold temperatures were associated with the reduced IENF densities (P = 0.032). In conclusion, cutaneous vasculitis and lupus activities underlie skin denervation with associated elevation of thermal thresholds as a major manifestation of sensory nerve injury in SLE.

Quantitative thermal sensory testing — value of testing for both cold and warm sensation detection in evaluation of small fiber neuropathy

OBJECTIVE

Small fiber neuropathy is a common neurological disorder, often missed or ignored by physicians, since examination and routine nerve conduction studies are usually normal in this condition. Many methods including quantitative thermal sensory testing are currently being used for early detection of this condition, so as to enable timely investigation and treatment. This study was conducted to assess the yield of quantitative thermal sensory testing in diagnosis of small fiber neuropathy.

MATERIAL AND METHODS

We included patients presenting with history suggestive of positive and/or negative sensory symptoms, with normal examination findings, clinically suggestive of small fiber neuropathy, with normal or minimally abnormal routine nerve conduction studies. These patients were subjected to quantitative thermal sensory testing using a Medoc TSA-II Neurosensory analyser at two sites and for two modalities. QST data were compared with those in 120 normal healthy controls.

RESULTS

Twenty-five patients (16 males, 9 females) with mean age 46.8+/-16.6 years (range: 21-75 years) were included in the study. The mean duration of symptoms was 1.6+/-1.6 years (range: 3 months-6 years). Eighteen patients (72%) had abnormal thresholds in at least one modality. Thermal thresholds were normal in 7 out of the 25 patients.

CONCLUSION

This study demonstrates that quantitative thermal sensory testing is a fairly sensitive method for detection of small fiber neuropathy especially in patients with normal routine nerve conduction studies.